Apparatus for measuring watts in electrical circuits.



PATENTED JAN. 16, 1906.

E. WILSON.

APPARATUS FOR MEASURING WATTS IN ELECTRICAL CIRCUITS.

APPLICATION FILED DEC.17, 1904 B SHEETS-SHEET 1.

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v PATENTED JAN. 16, 1906. E. WILSON.

APPARATUS FOR MEASURING WATTS IN ELECTRICAL CIRCUITS.

APPLICATION FILED DEC. 17, 1904 8 SHEETS-SHEET 2- E. WILSON.

APPARATUS FOR MEASURING WATTS IN ELECTRICAL CIRCUITS.

APPLICATION FILED 1330.17, 1904 8 SHEETS-SHEET 3.

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APPARATUS FOR MEASURING WATTS IN ELECTRICAL CIRCUITS. APPLICATION FILEDDEO.17, 1904 PATBNTED JAN. 16, 1906.

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. E. WILSON.

APPARATUS FOR MEASURING WATTS IN ELECTRICAL CIRCUITS.

APPLICATION TILED DEG.17,1904

8 SHEETS-SHEET 6.

PATENTED JAN.16, 1906.

E. WILSON. APPARATUS FOR MEASURING WATTS IN ELECTRICAL CIRCUITS.

APPLICATION FILED DEC. 17, 1904 8 SHEETS-SHEET 7.

W Mon 1 M fin/120% No. 810,179. PATENTED JAN. 16, 19%.

- A E WILSON, APPARATUS FOR MEASURING WATTS IN ELECTRICAL CIRCUITS.

APPLICATION FILED DBO.17, 1904.

8 SHEETS-QEHET 8.

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L W MMf/m M ERNEST WILSON, OF LONDON, ENGLAND.

APPARATUS FOR MEASURING WATTS IN ELECTRICAL CIRCUITS.

Specification of Letters Patent.

Patented Jan. 16, 1906.

Application filed December 1'7, 1904. Serial No" 237,275.

T0 at whom it may concern:

Be it known that I, ERNEST WILsoN, professor of engineering at KingsCollege, London, W. 0., a subject of the King of Great Britain, residingat 64 St. Johns Park, Blackheath, in the county of Kent, England, haveinvented a new and useful Apparatus for Measuring Watts in ElectricalSystems, of which the following is a specification.

In connection with the use of the quadrantelectrometer as a wattmeterfor alternating or direct current systems it has been usual to employ anon-inductive resistance placed in the work-circuit for the purpose ofproducing a potential difference to be applied to the quadrants of theelectrometer. This method of working involves the dissipation of acertain amount of energy in the resistance placed in the work-circuit,and when the current is large this dissipation becomes serious and themethod has drawbacks.

The present invention has for its object a modification of the systemmentioned above, by means of which the use of a special noninductiveresistance in the work-circuit is avoided, the potential for thequadrants of the electrometer being obtained from a secondary systemwhich is so affected by induction from the work-circuit that it willgiveto the uadrants a potential strictly proportiona l to and in phase(or opposition of phase) with the current in the work-circuit.

The best method of attaining the desired object is to employ a smalldynamo-electric machine driven at constant speed in a field produced bythe current in the worlccircuit, the armature of the machine thenfurnishing to the quadrants through a commutator and brushes thenecessary potential difference which is proportional to and in phasewith the current in the work-circuit. This method is applicable todirectcurrent systems as well as alternating. In a modification whenalternating currents only are dealt with the dynamo-electric machine maybe replaced by a coil in which a potential is induced from a primarycoil in the work-circuit, the said potential being applied throughsuitable regulating devices to the terminals of a condenser from whichthe potential difference for the quadrants is derived. The secondarrangement is substantially equivalent to the first, seeing that theinductioncoil and regulating devices, which in the second give aninduced potential in phase (or opposition of phase) with the current inthe work-circuit, have the same effect as the armature which is rotatedat constant speed in the form of apparatus first mentioned. In botharrangements the electromotive force in the secondary system variesdirectly as the current in the primary or work-circuit and is in phasewith it.

In the accompanying drawings, Figure 1 illustrates diagrammatically thearrangement for measuring the watts in an electrical system ofhigh-power factor. Fig. 2 shows the form of electrometer preferred foruse in measuring the watts in polyphase systems. Fig. 3 shows a diagramof connections for measuring the watts with this electrometer in atwophase system wherein one end of each phase winding in the generatingplant is earthed. Fig. 4 represents in a similar manner the diagram ofconnections as applied to a three-phase system. Fig. 5 illustratesanother method of working applicable to three-phase systems wherein thecenters of the phase windings in the generators are connected and may ormay not be earthed. Figs. 6, 7, 8, 9, 10, and 11 are detail viewshereinafter described, illustrating methods of obtaining from the smalldynamo-electric machine a connection for the case of the electrometerwhich shall give to the case a zero potential as compared with thepotentials of the quadrants. Figs. 12, 13, 14, and 15 are diagrams ofconnections hereinafter described, illustrating the method of obtain ingthe potential difference for the quadrants of the electrometer from asecondary circuit in which an electromotive force is produced byinducton from the work-circuit. This method is only applicable toalternating-current systems.

As is well known, the correctness of the reading with an electrometerused as a wattmeter in ordinary working depends upon the fact that thepotentials of the two pairs of quadrants above and below case are equaland opposite, so that the result obtained varies only as the averageproduct of (1) the potential of the needle and (2) the sum of thepotentials of the quadrants, or, rather, as the average product of (1)the potential of the needle and (2) the potential of either pair ofquadrants, seeing that both pairs are at equal potential above and belowcase, the potentials being in phase Now when working with high-powerfactors and high potential of the needle as compared with the quadrantsthe error introduced by making the potential of one pair of uadrantszero may be small, because the in ication then given varies with theaverage product of (1) the potential of the needle minus half thepotential difference of one of the pairs of quadrants and (2) thepotential of the one pair of quadrants, and the potential of the needlebeing high the subtraction from it in the vector sense of half thepotential difference of one of the quadrants makes a difierence whichmay be neglected. Calling the pairs of quadrants in the electrometer aand b and the needle 0, if the one pair of uadrantssay bis connected tothe case, w ich is taken to be at zero potential the readin given willvary with the average product of (1) the potential of the needle 0 minushalf the differ ence of potential of the quadrant a and (2) thepotential of quadrant a. If the voltage of the work-circuit is of theorder of, say, ten thousand, (square root of mean square volts,) thenthe potential of a can be small in comparison with quantity 1; but thisarrangement must not be used for very low-power factors, because theaverage watts with sine curves vary as the cosine of the angle'of lag(phase displacement) of the potential difference and the current in theWork-circuit, and the effect produced by putting one pair of quadrantsto case will be to cause avariation in the angle of lag so far as theinstrument is concerned. As the power factor is low, the angle isconsiderable and its cosine may be greatly affected thereby.

As the device forming the object of this invention is primarily desigpedfor measuring the watts in systems of 'gh-power factors, thearrangements first described will be those wherein the case of theelectrometer is connected to one of the pairs of quadrants and to thepoint in the work-circuit regarded as at zero potential. Themodifications necessary for insuring accurate indications on all powerfactors will be mentioned subsequently.

Referring first to Fig. 1, '0 and w are two lines or bus-bars in analternating system between points d and e in which the watts are to bemeasured. a and b are opposite pairs of quadrants in the electrometer. cis the needle of the electrometer connected to the point e, and f itscase. (Diagonallyopposite quadrants in the electrometer are connectedtogether, as is well known. The connections are not shown on thedrawings, because these latter are only intended to illustrate theessence of the present invention.) 41 is a coil in the work-circuitadapted to supply the magnetic field for the armature g of a smalldynamo-electric machine which is driven in the said field at a constantspeed by a synchronous motor or by an inductionmotor (deriving itscurrent from the workcircuit) or even by a separate direct-currentmotor, clockwork, or other mechanism of any suitable known type providedwith adequate governing means. This motor is indicated diagrammaticallyin dotted lines at 66 in Fig. 1. For clearness it is not shownseparately in the other figures of the drawings; but the letter 9 (or g9 is assumed to cover the motor-generator as a whole. The coil i must beof such construction that it is as nearly as possible devoid of skineffect due to induced currents in its massthat is to say, it may whennecessary be a strip or hollow'conductor or a conductor composed ofstranded wires insulated from one another, in which the exposed surfacesof the several conducting-wires are equal. In the event of a shunt beingemployed, so that the coil i only carries a portion of the current inthe work-circuit, care must be taken to make the ratio of resistance toself-induction the same in the field and shunt coils, respectively. Thearmature g has a commutator made up of a comparatively large number ofparts on which bear brushes h 70, connected, respectively, to thequadrants b and a. It is important to set the brushes h 76 on theneutral line in order that the electromotive force of the armature maybe that due only to the cutting of the lines of force by rotation of thearmature. If the armature is stationary, an alternating magnetic fieldproduced by the current in the field-coil should produce noelectromotive force between the brushes h k. By aid of a revolvingcontactmaker and an electrometer used in wellknown manner the brushesmay be set so that the electromotive force between them is zero when thecurrent in the work-circuit is zero. Under these conditions theelectromotive force of the armature has the same wave form as thecurrent in the work-circuit. Quadrants bare shown connected to the caseJ" and to the one point d in the work-circuit. The generator 9 containsas little metal as possible besides the armature and field coils, andthe coils 01 are in air or other medium of constant permeability.Practically no current passes through the armature of the generator. Itserves only to supply the necessary potential difference to thequadrants. Hence the energy dissipated in the armaturecoils will bepractically ml. The number of commutator parts should be such that waveforms of the current in the work-circuit can be accurately repeated inthe wave forms of the electromotive force of the armature as between itsbrushes. It has been found that one hundred commutator parts issufficient in a two-pole generator making one revolution per period tosuccessfully deal with wave forms deviating considerably from a sinecurve. The construction of the generator forms no part of thisinvention. A suitable type of such generator has been explained indetail in the complete specification of British Patent No. 5,582 of1904; but many other suitable forms o1 generator might be designed towork according to thisinvention. The electrometer also may have anysuitable internal construction. One suitable form of construction isdescribed in the complete specification of British Patent No. 2,707 of1904:. The electrometer, however, forms no part of this invention in sofar as its internal construction is concerned.

The system shown in Fig. 1 is obviously applicable to the'measurement ofwatts in directcurrent as well as alternating-current systems. Thearrangement for both purposes is the same. For a two or more phasesystem the watts may be measured by using other complete sets ofapparatus, each similar to that shown in Fig. 1, connected betweenpoints in the work-circuit conductors or bus-bars of the several phases,or the same set may be connected successively between the severalconductors. The readings so obtained must be added together to obtainthe total watts. The lines Q) and w, for instance, may be regarded astwo bus-bars for one phase in a two-phase system, and the samearrangement would be required between the two bus-bars of the otherphase, or 'U and to may be two of the busbars of a three-phase system,and another set of apparatus would then be required in which the needleof the instrument would be also connected at e-in bar w, and thepotential difference for the quadrants would be obtained by another genferator g, working in a coil i, connected to the other phase bus-bar.Such general arrangements will need no further explanation, as theycorrespond with those now usually em ployed with wattmeters operatingwith noninductive resistances in the work-circuit. It is possible,however, to avoid the inconvenience of having to add together thereadings of two or more wattmeters by employing an instrument in whichthe electrometers sepa rated by adequate insulation are mounted one uponanother, so that their needles are on one spindle whose movements aredue to the combined forces acting on the needles. The indications thengiven will be the total watts between the several phases of the system.An instrument of this character suitable for use as a wattmeter for twoor three phase systems is illustrated in Fig. 2. The upper and lowerparts 00 y (each a complete electrometer substantially of the type, forinstance, explained in the specification of British Patent No. 2,707 of1904) are separated from one another and from the ground by adequateinsulation inthe form of pillars 2'. The needles 9 10, one of which isindicated by dotted lines in each instrument, are mounted on spindlesrigidly connected at the center by an insulating-piece 11, which maycarry the mirror 12 or other means for indicating deflections. Theterminals for the needles are at 7 and 8, respectively, while 1 and 4are the two case-terminals, and 2 3 and 5 6 are the respective terminalsof the pairs of quadrants in the instruments insulated from the cases.If under any circumstances the two cases are to be at the same or zeropotential, the terminals 1 and 4 may be connected, while if the needlesin both instruments are to be at the same potential the terminals 7 and8 may be connected.

Fig. 3 shows diagrammatically the essential parts of the electrometerabove explained as applied by a system for measuring watts in atwo-phase plant wherein one end of each phase winding in the generatorsis earthed or connected to a common point p. The electrometer and itsterminals are lettered and numbered to correspond with Figs. 1 and 2,the letters in the lower instrument corresponding with those in theupper instrument being dashed. For the sake of clearness only the topand bottom portions of the quadrants are shown. The ends Z on of the twowindings in the generator are earthed or connected to a common pointat 1) after being carried by lines respectively, through the field-coilsi i of the two generators g g. The other ends n 0 of the windings goingto the bush-bars or mains are connected by lines 9 7", respectively,with the terminals 7 S of needles 9 10, which are thus respectively atthe potentials of the ends n 0. The brushes h h are connected to thecases f at 1 and 4, and these latter are connected together to thequadrants b b and to a point p, as indicated, which may or may not beearthed. The brushes 76 k are connected, respectively, to quadrants a a.With this system the reading of deflection of the connected needles 9 10will give directly the total watts.

Fig. 4 shows the diagram of connections for using the electrometer withconnected needles on a three-phase system. The main 16 from the end 13of one star (or mesh) in the generator contains the field-coil i ofgenerator g. The main 17 from end 14 of an other star (or mesh) containsthe coil i of the second generator g. The main 18 from end 15 of thethird star (or mesh) is connected to both terminals 7 8 of needles 9 10.The brushes 7c it" are connected to the quadrants a a, as before, andbrushes h h are connected at 1 4 to the casesff (to which also thequadrants b are connected) and also to terminals 13 14. The needles arethus at the potential of the terminal 15 and the cases-with thequadrants b b in each at the potentials of terminals 13 14,respectively, while the quadrants a a. differ in potential fromquadrants b b by the potential difference produced by the generators gg, which for a given value of the potential of the needle is sufficientto produce the desired sensibility.

The last-described arrangement is suitable for any three phase system.In one, in which the centers of the stars in the generators are earthedor connected to a common 3 point at 20 through lines 28, 29, 30, and 19in Fig. 5, the arrangement shown in that figure is applicable. Thisarrangement has the advantage that the case of the instrument and onepair of quadrants are earthed, rendering the apparatus easier to handle.Three generators g g g are required, each working in a field provided bythe currents in the lines 28, 29, and 30, respectively. The electrometermust now have in one case f (or three connected cases) three sets ofquadrants a b, a Z), and. (L 6 with three needles 9 2]. 10 insulatedfrom one another on a rigid spindle. The needles are connected to thethree terminals of the generator plant, 9 being connected by itsterminal 7 to 15, 10 by its terminal 8 to 13, and 21 (the intermediateneedle) to terminal 14 by an insulated conductor 22, connected to thestem of the needle by a flexible end piece 3].. The quadrants b I) b areconnected to the case], and this latter is earthed by lines 23 19. Thequadrants a a a are connected to the brushes 16 1c 76, and brushes h h hare earthed. The reading given by this instrument is the total Wattsbetween the three mains or phases.

In all the arrangements above explained one pair of quadrants isconnected to casean expedient only advisable when the power factor ofthe system is high. An arrangement such as those shown in Figs. 6, 7, 8,9, 10, or 11 must be adopted when working on very low power factors,where the connection of one pair of quadrants. to the case would introduce error.

In the arrangement shown in Fig. 6 the connections are exactly as inFig. 1, except that the brushes h are connected to quadrants b a,respectively, neither of which is joined, to case, and the casef isconnected to the middle plate of a condenser j, the outer plates ofwhich are charged by brushes h 10, respectively. The casef (which isalso connected to a point 01 in the main 1)) is thus at an intermediatepotential between those of the pairs of quadrants.

Fig. 7 shows an arrangement wherein the intermediate and relative Zeropotential for the case is obtained from a brush 32 working on thecommutator of armature g at the neutral point between brushes h and 7c.

Fig. 8 shows an arrangement in which a high non-inductive resistance areplaces the condenser j of Fig. 6, the casef being connected to thecenter of the resistance.

Fig. 9 shows an arrangement wherein the armature g has two complete andequal windings connected, respectively, to the commutators 24 25. Onebrush on each commutator is then connected to casef, while the otherbrushes go to quadrants a and b.

Fig. 10 shows a modification wherein there are two equal armatures g gon one shaft working in opposed fields of equal strength produced bycoils 2'' i (wound in opposite senses,) and each armature has acommutator 26 27. The brushes are connected together and to thequadrants just as in F ig. 9.

Fig. 11 shows how the brushes of two double armatures, such as thatshown in Fig. 9, but placed one in each of two opposed fields, as inFig. 10, may be connected to one another and to the quadrants in orderthat the electromotive forces between the case and one pair of uadrantsand the case and the other pair df quadrants, respectively, may be atall times equal and opposite in sign. 9 g are the two armatures. 70 71and 72 73 are their commutators. One brush of commutator 70 is connectedto quadrant pair 6 and the other brush to one brush of commutator 72.Similarly one brush of commutator 73 is connected to quadrant pair a andthe other to one brush of commutator 71. The remaining brushes ofcommutators 71 72 are connected together and to the case f. Thisarrangement has the advantage of astaticism, so that it can be used inplaces where there are magnetic fields other than the magnetic fieldproduced by currents in the coil i in the work-circuit.

In all the arrangements above explained if the motor 66 is of thesynchronous type and works in synchronism with the generators supplyingthe alternating current should the frequency of the current in thework-circuit vary the machine may still be made to give a potentialstrictly proportional to the said current if a portion of the latter betaken in a suitably-controlled shunt past the generator-coil i, or, whenthe motor 66 is of the induction type, its speed may be controlled, asis required, by varying the resistance in its armature in any suitableknown manner. In every case the speed of the generator must be keptconstant, or a correction must be applied to the wattmeter reading ifthe speed varies by known amount.

Referring now to the modified constructions illustrated in Figs. 12 to15, the same letters of reference have been employed for the parts whichare the same as in Figs. 1 to 11.

In Fig. 12, 48 is the source of alternating current connected bybus-bars or the like 1) 'w to the load 47. At any convenient point inthe Work-circuit is inserted the primary 33 of an induction-coilcontaining a very few turns and a number of smaller wire turns 34 in thesecondary. Preferably an air coil should be used, as iron or othersimilar me dium in the coil is objectionable because of its variablepermeability. The one pair of quadrants a of the electrometer isconnected to one end of the induction-coil secondary 34 through a wire35 and inductive resistance 36, while the other pair I) is connected tothe other end of winding 34 by wire 37 and inductive resistance-38. Thecase f of the instrument is connected by a lead 39 to the center of thewinding 34 and (as indicated by dotted lines) to a point in thework-circuit, while the needle 0 is connected by a lead 40 to anotherpoint in the work-circuit, it being required to measure the wattsbetween the said two points. The case of the instrumentf is alsoconnected to one side of each of two condensers 41 42, which through thelead 39 and resistances 36 38 make up two secondary circuits, eachincluding half of the winding 34. In the diagram plug-contacts 43 areshown for varying the capacities of the condensers41 42, switches 44 foradjusting the inductive resistances 36 38, and switches 45 for varyingthe mutual induction between the primary 33 and secondary 34. The saiddevices of course standfor any known means for varying the capacity,self-induction, and mutual induction. By equally adjusting either theself-induction or .the capacity, or both, in each of the two secondarycircuits, respectively, for a given frequency it is possible with simpleharmonic curves, as will be well understood, to cause the potentialdifference at the terminals of the condensers to be in quadrature withthe electromotive force impressed on the secondary circuit by mutualinduction from the work-circuit, and since this im pressed electromotiveforce is in quadrature with the current in the work-circuit thepotential differences between the terminals of each condenser may bekept equal and brought into opposition of phase with the current in thework-circuit. Since also the case of the instrument is connected to oneterminal of each condenser and the pairs of quadrants, respectively, tothe other terminals, the potential differences between the respectivepairs of quadrants and the case are equal and opposite in sign and haveamplitudes proportional to and are in phase with the current in thework-circuit. By this arrangement, therefore, results are obtained fromthe electrometer in the same way as by the usual method of measurement,but without the use of the usual non-inductive resistance in theworkcircuit. Moreover, since the potential difference between the caseand the quadrants may be many fold the potential difference between theends of the primary coil 33 the dissipation of energy in the coil 33 maybe very small as compared with the dissipation of energy which wouldoccur in a non-inductive resistance if the same potential differencebetween the case and quadrants had to be produced thereby. For a givenfrequency, then the self-induction and capacity must be adjusted, as iswell known, in order to bring about the result explained. The variationof mutual induction between the primary and secondary coils may beconvenient when varying power factors have to be dealt with. When thepower factor of the work-circuit is high, the

mutual induction can be made smaller than when the power-factor issmall; but for a given mutual induction and frequency the potentialdifference between the case and the quadrants can be varied in amplitudeby simultaneously varying the capacity and selfinduction, as is wellknown, and in such manner that the potential differences between thecase and quadrants, respectively, are still equal and in phase with thecurrent in the work-circuit, so that if it is not desired to vary themutual induction the adjustment can still be effected by variation ofthe self induction and capacity of the secondary circuit 34 in order tosuit the sensibility of the instrument. The condensers 41 42 should havea capacity large as compared with the capacity of the electrometer inorder that any variations in the latter may not cause the potentialdifference between the quadrants and the case to vary appreciably otherthan in direct proportion to the current in the work-circuit, both inamplitude and phase. The dielectric chosen should be such as todissipate little or no energy when subjected to varying displacementcurrents, and the insulation resistance between. the plates of thecondensers should be high. The portion of the work-circuit actinginductively upon the secondary circuit should be of such constructionthat it'is as nearly as possible devoid of skin effect, due to inducedcurrents in its mass-that is to say, it may when necessary be a strip orhollow conductor, or, preferably, a conductor composed of stranded wiresinsulated from one another, in which the exposed surfaces of the severalconducting-wires are equal. The secondary windings will preferably be asfar as possible surrounded by or embedded among the primary windings inthe work-circuit, seeing that the medium in which the coils are'placedis to be air or a medium of as far as possible constant permeability.

The arrangement shown in Fig. 12 may be modified in such a way as to useone sec ondary circuit instead of two while securing substantiallythesame effects. This is done by the arrangement shown diagrammatically inFig. 13. The work-circuit, means for mutual induction, and the inductiveresistance in the secondary circuit are the same as before and arelettered to corre spond with the lefthand part of Fig. 12. The condenser42 and resistance 38 are unnecessary, the lead 37 from quadrant I) beingtaken to the second terminal of the condenser 41, while the casef isconnected to a plate or plates 46 midway between the other plates of thecondenser and to the main conductor 1) and is thereby made to have anintermediate (and relative Zero) potential. In other respects theoperation of this system agrees with that of Fig. 12.

The arrangements of Figs. 12 and 13 are ICC suitable for use on systemsof all power factors; but when working upon systems of highpower factora simplification corresponding to that first described in thespecification is available-that is to say, the case of the electrometermay be connected to one of the quadrants. Fig. 14 shows such anarrangement applied to the system of Fig. 12. In this case the secondset of apparatus (shown in Fig. 12) for maintaining one quadrant pair 6at an equal and opposite potential (to the other pair a relatively tothe potential of the needle) is dispensed with, the quadrant b beingdirectly connected to the case f, on the one hand, and to the one set ofplates of the condenser 41 and the end of coil 34 on the other hand.This figure will require nofurther explanation.

The necessary potential diiierence for the quadrants of the electrometercan be obtained by connecting the quadrants and case across theself-inductive portion of the circuit but as this method is moretroublesome than the one above described the first method is preferable.In some cases, however, the

modified method may be available, and it is therefore explained. Thearrangement as applied to the system of Fig. 14 is shown in Fig. 15, thecorresponding parts being similarly lettered. The electrometer isconnected across the inductive resistance 36, and this and the condenser41 are so adjusted that the impedance voltage, which now gives thepotential difference to the quadrants, is in quadrature with theelectromotive force impressed by the work-circuit upon the inducing partof the secondary circuit and is therefore in phase with the current inthe workcircuit. This method, however, involves more difficultadjustments of the reactance, resistance, and capacity in the secondarycircuit, as will be well understood by an engineer.

What I claim is 1. Apparatus for measuring the watts in electricalsystems comprising, in combination with the primary conductors, asecondary electric system, means for producing between two points in thesecondary system a potential which varies with the current in the workcircuit and is always proportional thereto, an electrometer, meansconnecting the pairs of quadrants of said electrometer to the said twopoints in the secondary system, and means connecting the case and theneedle of the electrometer to the points between which the watts are tobe measured.

2. Ap aratus for measuring the watts in electrical systems comprising,in combination with the primary conductors, a secondary electric system,means for roducing between two oints in the secon ary system a potentialwhich varies directly with the current in the work-circuit, anelectrometer,

means connecting the pairs of quadrants of said electrometer to said twopoints in the secondary system, means connecting the case and the needleof the electrometer to the points between which the watts are to bemeasured, and means connecting one of the pairs of quadrants to thecase.

3. Apparatus for measuring the watts in electrical systems comprising,in combination with a plurality of primary conductors, a plurality ofsecondary electrical systems, means for producing between two points ineach such a system a potential which varies directly with the current inone of the primary conductors, a plurality of electrometers, meansconnecting the pairs of quadrants in each electrometer to the two pointsin one of the secondary systems, andmeans connecting the cases andneedles of the electrometers to the points between which the watts areto be measured.

4. Apparatus for measuring the watts in electrical systems comprising,.in combination with a plurality of primary conductors, a plurality ofsecondary electric systems, means for producing between two points ineach such system a potential which varies directly with the current inone of the primary conductors, a plurality of electrometers andinsulating means connecting the spindles of their needles together,means connecting the pairs of quadrants in each electrometer to the twopoints in one of the secondary sys-' tems, and means connecting thecases and needles of the electrometers to the points between which thewatts are to be measured.

5. Apparatus for measuring the watts in electrical systems comprising,in combination with a plurality of primary conductors, a plurality ofsecondary electric systems, means for producing between two points ineach such system a potential which varies directly with the current inone of the primary conductors, a plurality of electrometers, meansconnecting the pairs of quadrants in each of said electrometers to thetwo points in one of the secondary systems, means connecting the casesand needles of the electrometers to the points between which the wattsare to be measured, and means connecting one pair of quadrants in eachelectrometer to the case.

6. Apparatus for measuring the watts in electrical systems comprising,in combination with the primary conductors, a dynamoelectric machine thefield of which is produced by the current in the work-circuit,

'means for driving the armature of said machine at constant speed, asecondary electric system connected to the brushes of the machine, anelectrometer, the pairs of quadrants of which are in the secondarysystem, and means connecting the case and needle of the electrometer tothe points between which the watts are to be measured.

7 Apparatus for measuring the watts in electrical systems comprising, incombination with a plurality of primary conductors, a plurality ofdynamo electric machines through the field-coils of each of which theprimary current of one of said conductors is taken, means for drivingthe armature of each machine at constant speed, a plurality of secondaryelectric systems each connected to the brushes of one of the machines, aplurality of electrometers the pairs of quadrants of which are in therespective secondary sys tems, and means connecting the cases andneedles of said electrometers to the points between which the watts areto be measured.

8. Apparatus for measuring the watts in electrical systems comprising,in combina-' tion with a plurality of primary conductors, a plurality ofdynamo electric machines through the field-coils of each of which theprimary current of one of said conductors is taken, means for drivingthe armature of each machine at constant speed, a plurality of secondaryelectric systems each connected to the brushes of one of the machines, aplurality of electrometers and insulating means connecting theirspindles, the pairs of quadrants in each electrometer being connected inone of the secondary systems, and means connecting the cases and needlesof the electrometers to the points between which the watts are to bemeasured.

9. Apparatus for measuring the watts in alternating-current systemscomprising, in combination with two primary conductors carrying workingcurrents of different phases and two other primary conductors eachearthed at one point and connected to one end of a phase-winding in thegenerating-station, two dynamoelectric machines the field-coil of eachof which is connected in one of the earthed primary conductors, meansfor driving the armatures of said machines at constant speed, twoelectrometers and insulating means connecting the spindles of theirneedles, means connecting the pairs of quadrants in each electrometereach to one of the brushes of the dynamo electric machines, andconnections between the cases of the electrometers and earth, andbetween the needles of the electrometers and the respective primaryconductors carrying the working currentsn 10. Apparatus for measuringthe watts in alternating-current systems comprising, in

combination withtwo primary conductors carrying working currents ofdifferent phases and two other primary conductors each earthed at onepoint and connected to one end of a phase-winding in thegenerating-station, two dynamo-electric machines the fieldcoil of eachof which is connected in one of the earthed primary conductors, meansfor driving the armatures of said machines at constant speed, twoelectrometers and insulating means connecting the spindles of theirneedles, means connecting the pairs of quadrants in each electrometereach to one of the brushes of the dynamo electric machines, andconnections between the cases of the electrometers and earthbetween thecases and one pair of quadrants in each, and between the needles of theelectrometers and the respective primary conductors carrying the workingcurrents.

In testimony whereof I have signed my name to this specification in thepresence of two subscribing witnesses.

ERNEST WILSON.

WVitnesses:

HUBERT A. GILL, LEONARD E. HAYNES.

